Teletypewriter exchange system



May 19, 1942. A. R. BoNoRDEN TELETYPEWRITER EXCHANGE SYSTEM 9 sheets-sheet 1 ,Filed Dec. l, 1939 N0. l INCOMING TRUNK May 19, 1942. A. R. BoNoRDEN I2,283,410

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A. R. BONORDEN TELETYPEWRITER EXCHANGE sYsTEM Filed Dec. l, 1939 BUSY-HACK SIGNAL EQUIPMENT f 9 `sheets-sheet 8 NEG //v VEA/TOR A ./P. BONO/QUE N ATTORNEY A. R. BONORDEN TELETYPEWRITER EXCHANGE SYSTEM May 19, 1942.

Filed Dec. -l, 1939 9 Sheets-Sheet 9 /N VEA/TOR y A RBONORDEN y ATTORNEY Patented May 19, 1942 TELETYPEWRITER EXCHANGE SYSTEM.-

Allen R. Bonorden, Plainfield, N. J., assignor to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York Application. December 1, 1939, Serial No. 307,028

7 Claims.

This invention relates to a satellite switching center constituting a part of a teletypewriter or printing telegraph exchange system.

It is particularly adapted for use in an area where a number of teletypewriter subscriber stations are located and wherein the traiic and number of subscribers does not warrant-an eX.- change or central oice, for the reason that to keep an exchange, or central office, with the usual operating personnel would not be economically justiable. The alternative method oi extending individual subscribers lines with toll or long line equipments from the exchange, or central oiiice, directly to the subscribers stations would likewise not be economically justifiable. f

In accordance with the present invention a silent switching point, or center, is established to provide service to the subscribers in the area in question over a relatively small number of trunks extending to one or more of the nearest central offices.v In this Way a small number of trunks will provide, with little or no delay, adequate service to a larger number of subscribers stations. The connections between the trunks and the subscribers lines are completed bymeans of keys at a cordless switchboard located at the The number of trunks and switching center. subscribers lines furnished in this system depend on the number of subscribers stations in an isolated area and the capacity of the cordless switchboard.

The system herein involves:

(l) A teletypewriter exchange, or central, office and a teletypewriter exchange switchboard;

(2) A satellite ofce equipped With a teletypewriter cordless switchboard;

(3) Subscribers stations.

The usual maintenance or testing man or men at the satellite oiiice may perform the necessary switching thereat; it is contemplated thatthis will occupy but little of their time.

A required number of trunks connect the teletypewriter exchange, or central, office switchboard with the satellite switching center, and individual lines connect the subscribers stations with the satellite switching center. It is broadly within the scope of the invention that some of the trunks from the satellite switchingV center extend to one teletypewriter exchange olice and that the other trunks extend to one or more other teletypewriter exchange oices. Also it is within the scope that the trunks between the satellite and the teletypewriter exchange oiiice may operate on a. two-path, or two-conductor, polar basis, or over a single conductor,

though the system/described herein makes use of magnetically operated visual signals and4 drops for supervisory purposes, it is within the scope that lamp signals may be used for this purpose. If two-conductor trunks are employed, eachV of the trunks may terminate at the teletypewriter exchange oice switchboard in a manner disclosed in Fig. 8 of U. S. Patent 2,143,000, granted to W. W. Cramer et al., on January 10, 1939,V or if single-conductor trunks are desired, each trunk Operation of an incoming call In making a call from theexchange officeto a subscribers station, the operator at the ex,- change office switchboard uses aV cord circuit for plugging into a jack connected to an idle trunk which extends to the satellite switching center. The operator then impresses ringing current over either or both trunk conductors. The ringing current automatically causes the following functions at the satellite switchingcenter:

(1) A visual drop signal associated with the selected idle trunk operates;

(2) A motor of the attendants teletypewriter at the satellite switching center starts to operate;

(3) An audible signal responds;

(4) Sources of potential are furnished for the trunk repeater;

(5) Motor generator sets are automatically started to furnish operating current to the switching equipment and for transmission purposes.

The satellite attendant upon noting the operators signal operates an answer key associated with the callingv trunk to thereby connect the teletypewriter at the satellite switching center across the loop of the trunk repeater. The closure of the loop side of the repeater extinguishes the cord lamp at the distant exchange office switchboard which signies to the exchange of ce operator that the satellite attendant is ready to receive the number of the called subscrbers `'station'. The repeater in the trunk teletypewriter from the calling trunk. The cord lamp at the exchange oiiice` switchboard now lights indicating that that the connection to the called subscribers station has been established and that the exchange office switchboard operator may, when she is ready, transmit ringing current to cause to be operated a ringing guard lamp associated with the termination of the calling trunk at the satellite switching center and an audible signal common to all incoming trunks. The attendant upon noting the signals operates the ring keyA momentarily in the calling trunk vto send a ringing current to the. called subscribers station.

The subscriber at the called station in response to the ringing signal operates a power switch whereby the ringing signal is silenced, the subscribers teletypewriter motor is 'started and the station line conductors are now connected through the loop repeater to the calling trunk. The subscribers teletypewriter at the called station is in condition to receive the message.

, The exchange oflice operator may recall the satellite attendant by rst asking the subscriber at the called station to disconnect if the subscriber has answered. Under this condition the operator may ring as for a new-call which operates the visual drop signal and thus noties the attendant of the recall. The subscriber at the called station may recall the operator at the exchange oi`ce by operating a recall key whereby the cord supervisory lamp at the exchange office switchboard is lighted and when the recall key is restored and reoperated repeatedly the lamp is caused to flash. The subscriber at the called station disconnects by restoring the power switch which disables the teletypewriter, stops the teletypewriter motor and again connects the lsubscribers ringer to the line circuit. The cord supervisory lamp at the exchange oilice switchboard lights and at the satellite switching center a magnetically operated visual disconnect signal associated with the calling trunk operates together with the audible signal which is common -ble alarm issilenced, and the calling trunk restored to normal. The operator at the exchange oiice switchboard upon noting the light of the cord supervisory lamp is extinguished removes the cord from the jack of the calling trunk.

Operation of outgoing call When a call is originated at a subscribers stationthe subscriber operates the power switch whereby the lteletypewriter is connected across the loop or line circuitI and the teletypewriter motor and rectier (when provided) are operated as described hereinbefore for an incoming call. At the satellite switching center the audi- .ble alarm is automatically sounded, a magnetically operated visual signal associated with the calling line operates and the power control circuit is closed to furnish currentA for operation of the system and for transmission. The satellite attendant upon noting the signals connects the calling line to an idle trunk by operating a certain key which is in engageable relation with both the idle trunk and the calling line. The signals are restored to normal by the operation of the key and current is applied to the selected trunk to light an answer lamp at the exchange oiiice switchboard. The exchange operator thereupon plugs into the jack associated with the lighted lamp and is thereby prepared to communicate with the calling subscriber.

LOCAL CONNECTION Calling subscriber requests a local connection Should it be desired to interconnect for communication purposes two subscribers stations which are connected to the satellite switching center, the calling subscribers station is connected through the satellite switching center to the distant exchange office switchboard as just described. The exchange ofce operator asks the calling subscriber to disconnect until called. The

operator upon noting the lighting of the supervisory lamp indicating that the calling station is disconnected, signals the attendant at the satellite switching center. The attendant upon noting the operated visual signal in the calling trunk operates the answering key in the same trunk thereby connecting the attendants teletypewriter with the trunk and 'extinguishing the supervisory lamp at the teletypewriter exchange oiiice switchboard. The exchange office operator informs the satellite attendant that station A is calling station B. The satellite attendant successively op- .erates two keys one of which is in engageable relation with both the calling trunk and a local .extension trunk and the other of which is in engageable relation with both the local extension .trunk and the -called subscribers line circuit.

The local extension trunk which is common to all vincoming trunks is now connected to the called subscribers station, the calling subscribers station and the incoming trunk. The satelliteattendant then restores the answering key in the incoming trunk and the supervisory lamp in the exchange oiiice switchboard lights indicating that the ringing may proceed. The exchange operator rings momentarily to light the ringing guard lamps respectively included in the incoming trunk and the local extension trunk. Upon hearing the audible alarm and noting the lighted guard lamps, the satellite attendant rings both subscribers stations A and B by operating the ring key in both the incoming and the local extension trunk. When the subscribers of stations A and B respond, the ringing guard lamps for the incoming and the local trunks respectively become extinguished and the connection is ready for communication with the exchange operator supervising the connection as though it had been established through her cord circuit.

A feature of the invention is the use of a cordless switchboard at the satellite switching center whereby a call may be established by means of an operable key between any one of a plurality of subscribers stations and any one of a lesser number of trunks extending to a distant exchange oil'ce, and between any two of a plurality of subscribers stations connected to the one satellite switching center.

Another feature is the use of an extension trunk at the satellite switching center in conjunction with only one trunk from the exchange omce for establishing a connection between any two of a plurality of subscrib-ers stations.

Still another feature is the provision of a system hereinbefore described with all of the facilities of supervision at both the exchange oice and the satellite switching center.

Another feature is the provision of the system hereinbefore described with means for calling un attended stations. Y

Another feature is the provision of a system hereinbefore described with key operated means for sending a busy signal to the exchange ofce operator when the subscribers station to which a call is requested is busy and to the subscribers when all trunks are busy.

Another feature is the provision of remote control of the motor generator sets and the attendants teletypewriter at the satellite switching center from the teletypewriter exchange -oliice switchboard and any one of the subscribers stations.

Another feature is the provision of immediate ringing on a called subscribers station by the satellite attendant when requested to do so by the exchange oice operator.

Another feature is the means available for a call between two local subscribers stations that makes it impossible for the satellite attendant to ring one station and forget to ring the other.

The system as shown herein is suitably adapted to employ five incoming trunks and twelve subscribers stations although only four trunks and two subscribers stations are shown.

In the drawings:

Fig. 1 shows a block arrangement of the system wherein the central cnice equipment of the teletypewriter exchange system is shown in diagrammatic form as being located at a distant point X, the satellite switching center equipment at a localpoint Y and two subscribers stations A and B connected by line circuits to the satellite switching center;

Fig. 2 shows the relative arrangement of the various figures of the drawings;

Fig. 3 shows in detail the schematic circuit for the terminating equipment for trunk No. l connected by trunk conductors to the distant teletypewriter exchange, -cr central office equipment (polar relays 340 and 326 with their associated spark killers and wave shaping network constitute a telegraph repeater, well known in the art, which provides two-path polar transmission on the trunk side and open and closed transmission in a diierential balanced loop on theY station side) Fig. 4 shows in diagrammatic form the terminating equipment for trunks Nos. 2, 3 and 4;

v Fig. 5 shows in detail the schematic circuit for subscribers station A and the supervisory equipment and switching keys for establishing connections between station A and trunks Nos. 1 and 2;

Fig. 6 shows in detail the schematic circuit for the supervisory equipment and switching keys for establishing connections between subscribers station A and trunks Nos. 3 and 4. Also shown in detail are the schematic circuits for the audible alarm signal control equipment which is common to all trunks employed in the system, the switching key for connecting station A with an extension trunk which is also common to all incoming trunks and a busy-back key and an alltrunks-busy key for station A;

Fig; 7 shows in detail the schematic circuit for subscribers station B and the switching keys for establishing connections between subscribers station B and trunksv Nos. 1 and 2; also there is shown the schematic circuits controlled by test keys for trunks Nos. 1 and 2 and a key for maintaining an established connection between a station line and a trunk;

Fig. 8 shows in detail the schematic circuit for station B and the 'switching keys for establishing connections between subscribers station B and trunks Nos. 3 and 4; also there are shown the schematic circuits controlled by test keys for trunks Nos. 3 and 4, a switching key for connecting station B with the extension trunk and extension trunk test keys, a, busy-back key and an all-trunks-busy key for station B, and a key for maintaining an established connection between a subscribers station line and the extension trunk;

Fig. 9 shows the schematic circuit for the satellite attendants teletypewriter and busy-back signals; and t Fig. 10 shows in detail the schematic circuit for the extension trunk and themotor generator sets and control circuits therefor (polar relays l, HHG and |0l'l constitute a telegraph repeater, well known in the art, which provides open and closed transmission in a differential balanced loop on one side and open and closed transmission in a series connected loop on the other side).

For the other subscribers stations intermediate stations A and B, but which are not shown in the drawings, it is'assumed that additional equipment corresponding to that which is-stated herein as being respectively associated with stations A and B, will be provided and such additional equipment will be` in associable relation with each of the incoming trunks in the same manner as `the equipment associated with stations A and B. y l

A detailed description of the system will now be given usingincoming trunk No. 1 which comprises conductors 30! and 302.

The operator. at the distant exchange oice desires to establish a connection over incoming trunk No. l to one of the subscribers stations that is connected to the satellite switching center. Theoperator by plugging into an idle trunk jack at the exchange switchboard (not shown) and by operating a key, transmits an impulse of ringing current over either or both of line conductors 30| and 302, depending on whether the line is oi the single or double-conductor type as shown. In response to the ringing current, relay 303 operates and closes an obvious operating circuit for slow-to-release relay 304. Relay 304 upon' operating, causes slow-to-operate relay 305 .to operate. Because cfthe slow-tc-release and sloW-to-operate characters of relays 304 and 305, respectively, a transient current impulse over the line which operates relay303 momentarily is ineffective to initiate a connection. 1f relay 303 remains operated suiciently long, relay 304 eventually releases since its operating path is opened by the operation ofrelay 305.v Relay 304, upon releasing, completes a path for operating relay 306 and opens the operating circuit of relay 305. Relay 300, however, operates fast and thereby holds relay 3t5 operated. This arrangement assures that only one pulse is obtained from the lower armature and contact of relay-306 during one ringing interval,

Relay 306, upon operating, closesV at its upper armature and contact a circuit traceable from ground at the outer upperarmature and back contact of relay 301, upper armature and contact of relay 30B, outer upper armature and back contact of relay 308, then in parallel paths one extending through the winding of relay 3'09 to grounded battery and the other extending over conductors 3|0, through the winding of visual signal drop relay 50| to grounded battery. Relay 309 operates and locks up over a path extending over its contact and inner upper armature, conductor 3| I, to ground at the normally closed make-before-break contact of relay 301. Relay 309, upon operating, closes at its lower armature and contact 3|2, a circuit extending from ground, over conductors 3| 3 and 3| 4, through the winding of power relay 3|5 to grounded battery to operate relay 3|5, and contact 3|6 prepares a circuit for causing relay 3|1 to hold open its left-hand contact, as shown, as soon as telegraph battery is available on conductor 3|8. Also relay 309, upon operating, closes at its outer upper armature and contact 3|9, a circuit extending from ground over conductor 320, through the winding of the motor start relay 90| in the attendants teletypewriter 900 at the satellite switching center. Relay 90| operates and the resulting functions will be hereinafter described.

Signal drop relay 50| operates and causes a drop shutter to operate thereby providing for the attendant at the satellite switching center a Visual signal indicating that a connection over incoming trunk No. 1 is desired. Relay 50|, upon operating, closes at its armature and contact a circuit extending from ground, over conductors 502 and 60|, normally closed contacts at the left spring member of key 602, through the winding of relay 603, to grounded battery. Relay 803 operates and closes an obvious circuit for operating buzzer relay 604. Relay 804 operates to provide for the satellite attendant an' audible signal that a connection is desired. Retardation ccil 605 and condenser 600 reduce the possibility of noise being impressed by the self-interrupting buzzer relay 604 on telephone circuits which may be served by the same battery plant.

Motor generators started ing of relay |002 to grounded battery. Rectifier 322 which, upon energizing, provides direct current of positive polarity to conductor 324 and direct current of negative polarity to conductor 325, to transmit polar signals over the contacts and armature of send repeater relay 326 to the central office switchboard. Relay |002 which is of the slow-to-release type operates and at its lower armature and contact closes an operating circuit for relay |003 and at its upper armature and contact closes an operating circuit for slowto-operate relay |004. Relay |004 operates slowly for a purpose which will be hereinafter described. Relay |003 operates and closes at its armatures and contacts a circuit for connecting alternating current source |005 to motor generator sets Plus and Minus (Fig. l). Current of positive and negative polarities are now impressed on conductors POS and NEG, respectively; the negative current being now applied to conductor 3|8 through upper-winding of polar relay 3|1 whereby the relay armature moves away from its left-hand contact as hereinbefore mentioned and as shown in the drawing. After a short interval of time, that is, suiiicient to assure that the motor generator sets and teletypewriter motor 902 have attained full speed, ground is applied over the armature and contacts of slowto-operate relay |004 to conductors |006 and 40|, connected in series, for a purpose to be hereinafter described. Teletypewriter motor 902 started to operate when relay 90| closed at its lower armatures and contacts a circuit including power source 904. When relay 90| operated,

it closed at its upper armature and contact an obvious circuit for energizing printer magnet 9| 0 and the lower, or biasing, winding of polar relay 905.

Satellite attendant answers The attendant upon receiving the visual and the audible signal operates the answering key 503 in incoming trunk No. 1 and restores manually the shutter of drop 50| which silences the audible signal. The operation of the answering key 503 closes a circuit extending from grounded battery 802 ai; the lower outer righthand spring of key conductor 803, operated contact and spring of key 503, conductor 504. through the winding of relay 301, contact 321 to ground or to ground at the back contact and upper armature of relay 328. Should the incoming callbe on incoming trunk No. 4 instead of on incoming trunk No. 1, the ground on the spring 80| would have been connected in a circuit which would extend-over conductor 803 through the contacts of the lower numbered trunk answering keys, in chain, to the contacts of the No. 4 trunk answering key' which herein is designated 655; the answering key 503 for incoming trunk No. 1 would have been, under such circumstances, in its normal position.

Relay 301 operates and locks in a circuit closed at its inner upper armature and front contact. Relay 301, upon operating, opens at its upper make-before-break contacts, the locking circuit for relay 309. Relay 309 releases. Also relay 301, upon operating, substitutes at its upper inner armature and front contact a ground for maintaining power relay 3'|5 operated when relay 309 releases. Furthermore relay 301, upon operating, closes at contact 362 an obvious operating circuit for relay 329 which operates.

If by this time the power control circuit is closed at the armature and contact of relay |004, as hereinbefore described, relay 329, upon operating, will now extend the circuit including conductors |006 and 40|, over the outer upper armature of relay 329, conductor 330, through the windingof relay 328 to grounded battery. Relay 328 operates. Also relay 329, upon operating, closes at its outer lower armature and contact a circuit for operating slow-to-release relay 33|. Relay 33| operates to eiect the operation of relay 308. Relay 308, upon operating, replaces at its lower armature and contact, the ground connection for the upper winding of relay 3| 1 when such connection was opened by the release of relay 309. Also relay 308, upon operating, prepares at its upper inner armature and contact a locking circuit for itself which will extend, when completed, over the outer upper armature and back contact of relay 354, inner upper armature and Contact of relay 35| to ground.

Relay 328', upon operating, connects at its outer lower armature and contact a ground connection to the artificial loop consisting of resistances 333 and 334 and condenser 335 of the trunk repeater and at its inner lower armature and'contact a ground connection to bias polar relay 3|1 through its lower winding so as to cause relay 3|1 to make its left-hand contact. Also relay 328, upon operating, closes at its contact 336 an obvious operating circuit for relay 331 and at its upper armature and front contact connects ground to the contact of relay 338. Relay 331, upon operating, transfers trunk No. 1 consisting of conductors 30| and 302, from its back to its front contacts whereby trunk No. 1 is disconnected from relay 303 and conductor 30| is connected over conductor 339 to ground through 'the winding of the trunk repeater receive relay 340, and conductor 302 is connected over conductor 34|, through the winding of retardation coil 342, armature and left-hand, or space, contact of the trunk repeater send relay 326, conductor 325 to negative side of rectifier 322.

Attendants teletypewriter connected When relay 329 operated, as herenbefore described, the attendants teletypewriter 900 is connected to the operating winding of send repeater relay 326 in -a circuit traceable from motor generator set Minus (Fig. conductor NEG, through the lower winding of differential relay 338, inner lower armature and front Contact of relay 32S, conductor 344 including pad resistance 601, normally closed contact and right spring member of key 608, conductor 609, normally closed contact and left lower spring member of key 80|, conductor 804, shunt key 901, upper winding of polarized relay 905, normally closed make-before-break contacts of relay 908, conductor 909, inner normally closed contact and inner right lower spring member of key 80|, conductor 805, inner left spring member and nor-l mally closed contact of key 608, conductor 345 including pad resistance 8|0, front contact and inner upper armature of relay 329, through the upper windings, in series, of diierential relay 338 and polar relay 346, upper winding of repeater send relay 326, armature and right-hand,

or mark, contact of repeater receive relay 340, battery tap resistance 341, conductor POS,` to motor generator set Plus. Relay 338 does not operate but polar relays 346 and 320 close their right-hand, or mark, contacts.

Teletypewriter exchange operator receives signal to type called subscribers station number The closure of the loop side of the trunk repeater at the inner upper armature andfront contact of relay 329 and the operation of relay 331 causes positive current, which is marking in this case, to be applied to the trunk conductor 302 whereby the operators. cord lamp (not shown) at the teletypewriter switchboard at the exchange oice, becomes extinguished which signies to the operator at the exchange oiiice that she should type the number of the called subscribers station. The telegraph signals constituting the called subscribers station number operating on a polar basis over conductor 30| cause repeater receive relay 340 to repeat the signals to the attendants teletypewriter 900. When' the loop circuit ofthe trunk repeater is normally closed, relay 905 at the attendants teletypewriter is in its right-hand position as shown and the printer magnetv 9|0 is held operated in a circuit traceable from motor generator set V Minus` (Fig. 1o) over 'conductors `Nicci and en, armature anni right-hand contact of v'relay 905 through vthe' winding or" magnet 9|0 to ground at the Vupper armature and contact of relay-30|. In response to the rst space signal 'which constitutes the start impulse of the i'lrst character received from repeater receiverelay 340, relay 905 operates to its left-hand position under the influence of the Y received cause the number I0 to be typed on teletypewriter 900, operates key 506, which is the key on incoming trunk No. 1 that is assigned to subscribers station A. Key 506, upon being operated, disconnects station loop conductorsV 501 and 508 from the corresponding key for the other incoming trunks and connects them respectively to conductors 508 and 5|0, conductor 5|0 including the left-hand-spring member and normally closed contact of ringing key 5| the back contacts rand outer armatures of relay 5|2 and pad resistance 5|3. A ground at the contact and outer left spring member of key 500 is connected over conductor 5|4, upper armature and back contact of relay 348, through the winding of relay 349 to` grounded battery. -Relay 349 operates and at its lower armature and front contact connects a second ground over conductor 3 4 for maintaining power relay 3I5 operated. The priorground connected to conductor 3|4 for operating relay 3|5 is about to be removed when the attendant restores the answering `key 503.

Relay V349, upon operating, also extends the ground on conductor 40| over conductor 350, upper armature and Contact Vof relay 349, conductor 330, through the winding of' relay 328 to grounded battery. Relay 328 is thus lmaintained operated when the answering key 503 is restored. Teletypewrter exchange operator notified that Vcofmeetion has been established the attendant restores answering key503 to normal. Key 503, upon being restored, opens the operating circuit for relay 301 which releases and causes the release of relays 329 and Relay 90| released, shuts down the attendants teletypewriter. The release of relay 329 opens the operating circuit for Yslow-to-release relay y33| and transfers the loop conductors ofthe repeater from the attendants teletypewriter 900 to conductors 509 and 5|0 to which subscribersy station A is now connected. Since the subscriber at called station A has not las yet answered, loop conductor 5|0 terminates at the ringer and condenser at the station and loop conductor 509 terminates at ground at the station. Differential relay 338 operates and thereby causes relay 35| to operate.- Relay 35|, upon operating', provides through its inner upper 'armature and contact a locking circuit for relay 308. Relay 33| whose operating circuit was opened by relay 320, is suf; flciently slow to release to assure the locking cir-A cuit for relay 308 to be completed before thev operating circuit for relay 308 is opened by relay 33| releasing. Relay 35|, upon operating, also operates relay 352. Relay 352, upon operating, ktransfers the line conductors 30| and 302 from the trunk repeater to the winding of relay 303 and provides an articial line consisting of resistance 353 to hold relay 340in a marking, or right-hand, position. This transfer of the line conductors causes the cord lamp at the operators position at the distant teletypewriter exchange switchboard to be lighted as an indication that connection has been established to the called subscribers station A and that the exchange office operator may ring the station when she is ready to complete the connection.

Teletypewriter exchange operator indicates that called station A is to be rung When the operator rings, ringing current over the line conductors 30| and 302 causes relays 303, 304, 305 and 306 to operate in a manner hereinbefore described for an incoming call signal. Relay 306, upon operating, closes a circuit extending from ground at the outer upper armature and back contact of relay 301, over the upper armature and contact of relay 306, outer upper armature and front contact of relay 308, inner upper armature and contact of relay 354, a common point 355, through the winding of relay 356 to grounded battery. Relay 356 operates and closes an operating circuit for relay 354 which extends from grounded battery through the winding of relay 356, common point 355, through the winding of relay 354, contact and inner upper armature of relay 356, inner upper armature and contact of relay 35|] to ground. Relay 354 does not, however, operate at this time because of the shunt to ground at the common point 355. VAlso relay 356, upon operating, closes a. circuit extending from ground, lower armature and contact of relay 356, the lower armature and back contact of relay 354, conductor 351, left spring member and contact of key 602, through the winding of relay 603, to grounded battery. Relay 603 operates and thereby operates buzzer 604 to provide an audible alarm for the attendant. The audible lalarm persists until relay 354 operates. Also when relay 356 operated, another circuit was closed from grounded vbattery, through ringing guard lamp |5, conductor 5I6, outer upper armature and contact of relay 356, outer upper armature and contact of relay 35|, to ground. When eventually the ringing period controlled by the operator at the exchange oiiice is terminated, relay 306 releases and thereby removes the ground from common point 355 to permit relay 354 to operate over the path hereinbefore described as being prepared, or closed, by relay 356. Relay 354, upon operating, causes relay 308 to release so that a subsequent ringing signal can act to recall the attendant as hereinafter described. Relays 354 and 356 together provide a holding path to prevent polar relay 3|1 from closing its left-hand contact at this time which it would otherwise do when relay 308 released. i

Satellite attendant rings called station Lamp 5|5 lights as an indication that the attendant should ring momentarily on` the connection established for the calling` incoming trunk No. 1. Thisis accomplished by operatthe upper `spring member of key 5|8 to ground.

TheA audible signal indicates to the subscriber at station A that a message awaits and that he should operate start key 5|8 to connect his teletypewriter to the line circuit comprising conductors 501 and 508.

Subscriber at called station A answersV When the subscriber at called station A 'answers by operating start switch 5| 8 and alternating current power source 5|9 is connected to start the printer motor 520 and the printer magnet 52| and transmitting contacts 522 are connected at the operated contact and upper spring member of switch 5I8 to the line circuit comprising conductors 501v and 508. The power switch 5|8, when operated, also short-circuits the operating circuit for ringer 5|1.

Should the called subscribers station be of the type which requires a polarized relay to obtain satisfactory transmission over long loops such as that designated station B in Fig. '1, the circuit requirements will be slightly diiterent fromrthose shown for station A. Let it be assumed that a call incoming over trunk No. 1 is for station B. In that event key 10| instead of key 506 will be operated whereby the loop conductors 509 and 5|0 of the incoming trunk repeater will be respectvely connected to line conductors 102 and 103 and the ringing current applied at key 5H by the attend-ant at the satellite switching center will flow over conductor 5|0, operated contact and right-hand spring member of key 10|,

conductor 103, normally closed contact of recall key 103, through the path including ringer 105, to ground at the normal contact and left-hand spring member of switch 106. In response to the operation of ringer 105, the subscriber at station B will operate power switch 106 to connect an alternating current source 101 to operate the teletypewriter motor 108 and rectifier 109, and to short-circuit ringer 105. The operation of power Vswitch 106 also places the lower winding of polarized relay 100, break key 1|0, and sending contacts 1|I across line conductors 162 and 103. The rectier 109 furnishes .direct current for biasing polarized relay to its righthand, or marking, contact and operating current for printer magnet 1 |2.',

The closure of the line conductors and the removal of ground at the normally closed spring member of either of power switches 5| 8 or 106 depending upon which of stations A and B is engaged in the connection, cause -polar relays 346 and 326 to close their right-hand0r marking, contacts and cause differential relay 338 to release thereby releasing, in turn, relay 35|. Relay 35|, upon releasing, extinguishes ringing guard lamp 5|5 and releases relay 352 which reestablishes the transmission path between the trunk `conductors 30| and 302 and the ktrunk repeater which includes conductors 339 and 34|. Positive, or `mark, battery at, right contact of repeater send relay 326 is therefore connected to trunk conductor 302 which extinguishes the cord lamp at the exchange Oice indicating to the operator that communication' may proceed.V

Also relay 35|, upon releasing, releases relays 354 and 358. The removal of ground from the upper, or operating, winding of-relay 3|1 which was applied by relays 354 and 356, is now replaced by a ground at relay 343. Although relay 345 follows signals transmitted by thel subscribers station, the capacity of condenser 358 and the associated networks is such as to cause relay 3|1 to hold its left-hand contacts open for an appreciable length of time so that even through the station attendant may break for as long as three seconds, relay 3|1 will remain operated.

Exchange operator recalls After connection has been established and answer key 503 is restored as hereinbefore de scribed, the attendant has no further control over the connection nor will the operation of answer key 503 again connect a teletypewriter to the incoming trunk No. 1 for the reason that no ground is supplied to the winding of relay 301. However, if the exchange operator desires to recall the attendant at this time, she may do so by first asking the subscriber at called station A to disconnect if the subscriber has answered. Under this condition the exchange operator may ring as for a new call, operating the signal drop 50| and thus informing the attendant that she is wanted. The recall of the satellite attendant is hereinafter described in connection with establishing a local connection.

Station subscriber recalls The station subscriber may recall by repeatedly operating a recall key such as |6 at station A or 133 at station B. The recall key, upon being operated, opens one of the line conductors and then connects ground to it. Under this condition, relays 326 and 346 are held marking, that is, in their right-hand positions and the differential relay 338 operates causing relay 35| to operate. Relay 35|, upon operating, causes relay 352 to operate and thereby to transfer the trunk conductors and 302 from the trunk repeater. This condition causes the cord supervisory lamp at the operators switchboard at the exchange oiice to light. Each time the station subscriber restores the recall key, relays 338, and 352 release. This condition causes the lighted supervisory lamp at the exchange switchboard to ash.

Station subscriber disconnects When the station subscriber disconnects by restoring the power switch, such as 5|8 at station A or 105 at station B, power supply circuit to the teletypewriter motor and rectier at the station is opened. The line conductor is again placed in series with the condenser, ringer and ground and the other conductor is again grounded at the station on the tip side. Relays 338, 35|, and 352 operate as for a recall signal but relays 346 and 326 now go spacing and thereby close their left-hand contacts. This condition causes the lamp at the exchange switchboard to light. After an interval, relay 3|1 will release to its left-hand position to close a circuit extending rom ground at 4the upper armature and front contacts, in series, of relay 328, armature and left-hand contact of relay 3l1, outer lower armature and contact of relay 352, through the lower winding of relay 348, to grounded battery. Relay 358 operates and transfers conductor 5|4 by means of the upper armature of the relay from its back vcontact to its front contact thereby ing of the relay, conductor 350, normally closed contacts of relay 33| to grounded battery. The operating circuit for relay 349 is thereby opened and relay 349 releases to close a circuit from ground, lower armature and back contact of relay 349, front contact and `lower armature of relay 348, conductor 36|, through the winding of drop signal relay 523, conductor 524, right-handl spring member and normally closed contact of key 602, through the wnding of relay 603, to grounded battery. Drop signal relay 523 'operates to give a visual signal and relay 603 operates to lclose the operating circuit for buzzer relay 604 to give an audible signal. Relay 349 released, also opens at its lower armature and front contact, the operating circuit for relay 3|5 and its upper armature and contact, opens the operating circuit for relay 328. Relay 3|5 releases. Relay 328 releases and at its upper armature and lower front contacts-opens the operating circuit for relays 331 and 35| which release. The trunk is now prepared toreceive another incoming c all.

Relay 3|5, upon releasing, opens the power supply circuit for rectifier 332 and removes ground from conductors 323 and |00| in series. If no other call is in progress, i. e., no other ground on conductor |00|, relay |002 releases and opens the operating circuits for relays |004 and |003. Relay |003, upon releasing, opens the power supply circuit for motor generator sets Minus and Plus. Relay |004, upon releasing, disconnects at its lower armature the ground Satellite attendant disconnects station The attendant upon noting the visual disconnect signal at drop relay 523 associated with incoming trunk No. 1, restoresthe station key such as 506 for station A or 10| for station B which transfers the line conductors Afrom incoming trunk No. 1 causing relay 338 to release and removes ground from conductor 5|4thereby opening the locking circuit for relay 348. Relay 348 releases andopens at its lower armature and contact the operating circuit for drop signal relay 523 and relay 603. Drop signal relay 523 releases and restores the visual signal. Relay 603 releases and silences the buzzer or audible signal. The trunk is now restored to normal.

OPERATION or OUTGoING GALL Station subscriber originates a call When the station subscriber operates the power switch such las switch 5| 8 atv station A or 10S at station B the subscribers teletypewriter circuit is closed across the loop and the teletypewriter motor operated as described hereinbefore for an incoming call. Also, a rectier is energized if station B is considered. A circuit is completed extending from ground, through rectier 806, through one of several chains of switching keys, the chain depending upon which one of the subscribers stations is employed for originating the call. Should it be assumed that the subscriber at station A originated a call, the circuit may be traced over conductor 801, the normally closed contact and right-hand springV members of keys V(5|4, 6|5, BIB, 6|1, 525, and 506, in series, conductor 508, the normally closed contacts ofv recall key 5 I 6, operated contact and upper spring member of switch 5|8, through the winding `ofprinter closing a locking circuit through the upper Windmagnet 52|, normally closed contacts of break key 526, sending contacts 522, conductor 501, left-hand spring members and normally closed contacts of keys 506, 525, 6|1, 6|6, 6|5 and 6|4, in series, through the winding of drop signal relay 6|8 and resistance 6|9 in parallel, conductor 620, through the winding of relay |001 to ground. Relay |001 operates and contacts at its lower armature an operating circuit for power supply relay |002 whereby motor generator sets Plus and Minus are operated, and at its upper armature completes a circuit extending from ground, conductors |008 and |009, right-hand spring member and normally closed contact of key 602, through the winding of relay 603 to start the buzzer for an audible signal. The operating circuit for relay |001 also operates drop signal re, lay |8 which gives to the attendant a visual signal that a connection is desired at subscribers station A.

Satellite attendant connects the calling station to an idle trank The satellite attendant upon noting the signals selects an idle trunk extending to the distant exchange oiice and operates the calling station key which is assigned to the selected trunk. Assume that trunk No. 1 is idle and inasmuch as it is assumed that the call originated at subscribers station A, the attendant operates key 506. The operation of key 506 connects conductors 501 and 508 to trunk conductors 509 and 5|0, respectively. Key 506, upon being operated, disconnects visual drop signal 6|8 and relay |001. Drop signal relay 6|8 restores to normal and relay |001 releases whereby the audible buzzer signal provided by buzzer relay 604 is silenced. Key 506, upon being operated, closes a circuit extending from ground, outer left-hand spring member and operated contact of key 506, conductor 5|4, upper armature and back contact of relay 348, through the winding of relay 349, to grounded battery. Relay 349 operates and thereby connects at its lower armature and front contact a ground connection to the circuit extending over conductor 3 |4 through the winding of relay 3|5 to grounded battery. Relay 349, upon operating, also connects at its upper armature and contact, grounded conductors |006, 40| and 350, in series, to the winding of relay 328, over conductor 330. Relay 3|5 operates and at its upper armatures and contacts closes an energizing circuit for rectifier 322 and at its lower armature and contact connects ground through a circuit extending over conductor 323 and |00| through the winding of slow-torelease power control relay |0021 to grounded battery thereby preventing the power control circuit controlled by relay |002 from restoring to normal after relay |001 is released. n

Motor generator sets Plus and Minus upon attaining their full speed apply a full voltage to the upper windings of polar relays 346 and 326 and both relays are thus maintained in the positions shown, that is in the right-hand position. Relay 328, upon operating, energizes the biasing windings of polar relays 346 and 326 as hereinbefore described and causes relay 331 to operate which transfers the trunk conductors 30| and 302 from the winding of relay 303 to the respective Winding and armature of trunk repeater polar telegraph relays 340 and 326. Since the subscribers station loop is closedv differential relay 338 remains unoperated. f Polar relay 3|1 therefore opens its left-hand contact if it was not already opened before. l

Exchange oyce operator answers The closure of the trunk conductors 30| and 302 in the manner described causes the terminating equipment at the exchange switchboard to function and light the answering lamp associated with the trunk jack at that switchboard. When the exchange operator plugs into the trunk jack her cord supervisory signal will remain out and she will be in communication with the calling station which in this case is station A.

The calling subscribers station may recall as hereinbefore described for incoming calls without bringing in any signal at the satellite switching center.

When the calling subscriber disconnects, the circuit will function as hereinbefore described for disconnection on an incoming call.

OPERATION Fon Es'rABLIsHINc A LocAL CONNECTION Calling subscriber requests a local connection Assume that the subscriber at station A has initiated the call and that his line circuit has been connected to the operators switchboard at the distant exchange oflice in the manner hereinbefore described. Let it be assumed further that the operator at the distant exchange office has answered and that the subscriber at station A has indicated that he wished to have his line circuit connected to that of another subscribers station, say station B, served from the same satellite switching center. Under these conditions the operator at the distant exchange oiice will ask him to disconnect his line circuit until called. This request is made in order that the operator at the distant exchange ofce may recall` the attendant at the satellite switchina center.

Teletypewriter exchange ojice operator recalls As soon as the operator at the exchange oice notes that the cord lamp associated with the trunk is lighted as an indication that the subscriber at the calling station has disconnected,

the operator will immediately ring over the trunk circuit to the attendant at the satellite switching center. l

The ringing current will cause relays 303, 304, 305 .and 306 to operate as hereinbefore described. Relay 304, it will be noted, provides, upon operating, a holding ground for relay 3|1 so that even though relay 346 has opened its left-hand contacts when the calling subscriber is connected and relays 338,A 35| and 352 operated to provide Shutter of drop signal relay falls and satellite attendant answers With relay 306 operated, relay 309 operates as hereinbefore described and drop signal relay 50| is energized causing its shutter to fall and energize the audible alarm circuit comprising buzzer relay 604. The satellite attendant answers by operating answering key 503 thus connecting her teletypewri-ter 900 to the loop -repeater and causing the supervisory lamp at the exchange switchboard to be extinguished as hereinbef-ore described for an incoming call.

Teletypewrzter exchange operator types order The exchange oiice operator thereupon .types the order such as station A calling station B.

Satellite attendant connects extension trunk The satellite attendant thereupon operates the extension trunk key v52-1 whichis associated with trunk No. 1 in order to associate Athe extension trunk |000 with trunk No. lover which the order came. Key 521 upon being operated also ,connects .ground to .conductor '5M over its right- .hand spring .member and operated contact so that relay '34.9 .is .now held operated from both keys 521.and 506. YKey.521, in an operated position, closes at its .inner right .hand spring member and .operated contact, Va 4circuit extending from -ground through the winding of relay |010, conductor I, inner right spring member and operated contact of relay :521, Aconductor 528,

.through .the Winding o'f extension ,trunkiconnect- Plus. .Polar .relays -I 0I5 :and |.0 I 5 .are thus. energized .to.hold their left-hand,..or marking,.con

tacts closed. .Relay 1|.0I0 atitsouter upperar- .mature connectsgroundto the articialline of .the extensionmepeater.consisting of resistances .idle -andlil'land condenser .I02I whichfiscon- .nectedto .tlfietbiasingr orlower windings,in. series,

. ating, also .through its lower .armature and as- .sociate make .contacts .connects fthe biasing, or lower, winding 4of .relay.l0|1 .in series Ywith `re- -sistance |.0l8 to conductorNEGandalso .through resistance |033 to y,the 4space contactof polar relay l0 I 5 whose. armature :is .connected vtoconproportioned thatpolar relay-|0|.1 is biased .t0- ward its spacing -.or .marking 1 contacts .respectively `whenpolar relay I 0 I 5 is .markingon spacing. Hence when ipolar .relays |.0|,5 .and ,|0I5

Differential relay Y causes the operation of relay 102,6. Relay 1026,

.upon operating, closes atits lowerarmature and .iront contactan oporatingcirouit forrrelay |021 extension trunk relay associated with .trunk N9.- 2 ,and Ltlien,in turn, the back contacts and inner armatures of `each of the extension trunk relays associated with Atrunk No. 3, etc. so Vthat it is Anot possible to associate conductors |022 Iand |023 with more than one trunk at a time, the lower numbered trunks having the preference.

Satellite attendant `connects culled station line Ifhe .satellite attendant also operates "key -8 |0 which vis the called station key associated with extension vtrunk |000, to connect the called station B with the extension trunk |000. Key 8|0, in an operated condition, transfers `station line conductors .102 and 1 03 which are extended Ythrough .the normal contacts, .in series, of the lindividual incoming trunk ykeys associated with station AB, .from ythe drop. signal rel-ay 81| `and rectier 806 to conductors 81I2 and 8|3, yrespectively; there being included lin conductor 8|3 a ringing control spring member .of ring key 162|.

,Differential relay |024 operates in a circuit trace,- `able from motor generator set Minus, conductor NEG, battery tap resistance |025, 'through the lower winding ofre'lay |024, conductor 8|2, operated contact `and inner .left .spring member of ,key 18IY0, normally closedcontact and .innerjleft spring members vof each of Ykeys 8|48,|5, 113,110 I., in series, station line conductor 1 02, transmitting .contacts 1| I, normally closed contacts vvof break :key 'H0 .through .thelower winding of polarized relay" 100, left-hand e spring Vmember iand .normally closed contacts of power switch 106 t0 ground. |024 `operates .and `thereby whichris ofthe slowrelease type. .Relay |021, upon operating, .prepares v`an operating circuit `ior'tl'le,subsequent operation of relay IOI4. Relay |026, upon operating, prepares at A.its upper armature a i locking circuit for .relay 102.8.

-The Vsatellite .attendant then .restores answering,key.503 wh ich.results,in relays 3.01, .329 and V3.3i `being restored, in sequence. ,Howeven-as hereinbefore described, the. closure of therepeater ,to the .openstation line conductors such as 501 and .508 causesdifferential relay. 3.38 to 0p- -erateand in .turn operateswrelayf35l. l `upon operating, :provides .a locking jpath fori relay.30.8 `.which was previously operated by Aslowtoreleaserelay33| `so that the releaseofrelay follow .signals irom.stationB, .although :relay Il opens the upper-winding ,of-relay .|.0|I;v.re lay IBI? will 'hold its .marking .contactclosed However, when the vcurrentin thenpperwinding of relay IOI1 .is opened bystation Aortheexchange `.operator .sending a space signal, ...thef relay armature will `move 'to thespace `.contact under the .bias condition'in 'the lower winding.

Yltelay 5I2, .upon operating`inserts.`the .upper winding ofpolarized relay l0|1 andthearmature and left-hand, ,or.mark, contact of irelay |015, in series, with conductor 5|0,at.the same time 'removing the equivalent .resistance .5|3. The upper winding .of relay' |0|1 andthelefthand'contact of relay. |0|6 .arethus connected in series with conductor .510.by means-oi conductors |622 and |023, respectively. .It is noted that conductors |022 and |023 normally include, in regular order, i-lrst, the back contacts and inner armatures .ofthe extension-.trunk relay- 5 2 which is associated .with trunk. No. ,1,.-secondly,

the 'back contacts .and inner armatures of the,y

33| at this time leaves relay 308. operated. Since relay A.1t-52 operatesffrom relay '35| the cord-lamp at the exchange office switchboard lights `asan indication v.that ringing v,may proceed.

'Exchange cce operator rings on trunk When ,the .exchange .oice operator .rings momentarily, the end ofthe ringing periodleaves relays .3,54 and `3.50 operated and rlngingguard .lamp 5 I 5 lighted as hereinbefore described for an incoming call. ,In this case relay|029 .alsooperates-at the beginning of the ringing period in a -circuit .traceable from grounded battery through -the winding ofrelay |029,conductor |030, outer left .spring member andoperated contact of. key 521,

conductor .529, front ycontact-,andinnerupper rverat'ingat the .beginning-of the lringingpulse .initiated byrthe Aexchange .operator.

,Relay y 029, .upon opera-ting,` causes relay |028 to loperate over an obvious circuit. Relay |028 locks through its upper Winding to ground at relay |025 which is in an operated condition at thistime. The ground at the upper armature of relay |026 is connected in a circuit traceable over the front contact and `upper armature of relay |026, conductor |03|, inner left spring member and operated contact of key 521, conductor -530, through the winding of relay 352 to grounded battery. The circuit just traced serves thev purpose of holding relay 352 operated until the subscriber at called station B answers. Relay |028, upon operating, also completes a circuit for operating ringing guard lamp 622.

The satellite attendant upon hearing the momentary audible signal produced by buzzer relayV 604, notes the lighted guard lamps and rings both stations A and B by operating momentarily keys 5|| and 62|. These keys, when operated, respectively connect ground to conductors 520 and |030 which has no effect at this time. Each key also connects ringing current source 6|| to the ringer 5| 1 at station A and ringer '|05 atstation B causing the bells to ring.

When the subscriber at station A answers by operating start switch 5|8, polar relay 346, closes its right-hand, or mark, contact and differential relay 338 releases thereby releasing relay 35| which in turn releases relays 354, 356 and |029. Relay 352 does not release since it is also held operated in a circuit extending from relays |026 and |028 over conductors |03| and 530. Relay 35|, upon releasing, opens the operating circuit for ringing guard lamp 5|5 which consequently is extinguished.

When station B answers, differential relay |024 releases thereby releasing relay |026 and 'in turn relay |028 and extinguishes the ringing guard lamp 622. Relay |026, upon releasing,

also 'opens the operating circuit of sloW-to-release relay |021 and closes a circuit at its lower armature and back contact to operate relay |0|4.

vRelay |0|4 operates and closes at its lower armature and back contact, alocking circuit for itself before relay |021 eventually releases. Relay E |0|4, upon operating, extends the ringing side,

that is, conductor 103, of the loop circuit of station B, over the right-hand spring members oi' 623, through the Winding of relay |024, upperi armature and front `contact of relay Relay |026, upon releasing, disconnects at its upper armature and upperfront contact, ground? from the operating circuit for relay 352 and if the subscriber at station A has previously answered as was assumed, relay 352 will therefore release, closing through the telegraph transmission paths to the switchboard at the distant exchange office. This extinguishes the operators cord supervisory lamp at the exchange omce switchboard. The subscribers at stations A and B and the. operator at the exchange oflice are now in communication.

The subscriber at the calling station A may recall the operator in the distant exchange oiiice in the manner previously described herein, providedthe `called station has not disconnected. If the called station disconnects first, the operator at the exchange oice receives no signal but the calling station teletypewriter runs open.

When the subscriber at the called station B disconnects, polar relays |0|6 and |0|5 operate through their right-hand positions, the former opening the loop of the calling station A thus causing polar relays 346 and 326 to move their armatures to their left, or spacing, contacts. When the subscriber at the calling station A disconnects before or after the subscriber at the called station B, differential relay 330 operates and the sequence of events previously described for an incoming call occurs except that the satellite attendant upon noting the operated vsual disconnect signal 523 must restore both keys |0| and 521 before the visual signal becomes normal.

Key 521, upon being released, opens the operating path of relays |024, 5|2, and |0|0 which release. Relay 5|2, upon releasing, dissociates the extension trunk |000 from trunk No. l. Relay |0|0, upon releasing, restores relay |0|4 to normal and completes a path at its inner lower armature and back contact extending from grounded battery through the relay 603, contact and right-hand spring of key 602, conductor |000, inner lower armature and back contact of relay |0|0, conductor |032, through the winding of the visual drop signal relay 624, conductor 62 5, contact and outer left-hand spring member of key 8|0 to ground. The visual drop signal relay remains operated until the station extension trunk key 8 0 is restored to normal at which time the audible signal controlled by operated relay 603 will be silenced if no other calls are awaiting attention.

Calling an unattended station Unattended station circuits, well known in the art, are arranged so that a prolonged ringing period (about nine seconds) is effective in automatically operating-the station power connectingv relay thus starting the teletypewriter motor and connecting the station to the loop circui. When the called station served by the satellite switching center is of this type and fails to answer the regular ring, the calling station subscriber may indicate to the exchange office operator that he wishes to send unattended in which case the exchange oflce operator will recall the satellite v attendant in the manner hereinbefore described and types ring unattended. The satellite attendant after restoring the answer key will operate the ring key, such as key 5| in trunk No. 1

vand hold it operated. This will cause the ringing guard lamp 622 to immediately light as hereinbefore described. After an interval of about nine seconds, the called station will be automatically connected to the line in which case diierential relay 338 will release causing relay 35| to release and extinguish lamp 5| 5. The satellite attendant upon noting this, will release the ringing key such as 5||. Relay 35|, upon releasing, causes the release of relay 352. Relay 352, upon releasing, closes trunk conductors 30| and 302 through for transmission. The exchange I operators cord lamp is extinguished notifying Called station Zine busy When the satellite attendant receives an order on an incoming call for a station which is found to be busy, she will hold key 8|6 operated for 1 ductor NEG tomotor generator set Minus.

about two :seconds :.after x which ;,the .answering nkeyjs;restored. A''hisoonnects, a source 9590i interruptions to .the :iattendants L teletypewriter connects vat its inner `lower and its upper lowerv armature -and respective `front contacts, the right-hand contact of relay'914 -in series `with the i -attendants 'teletypewriten VPolarizedrelays V914 and l918'function-to 'generate a source of Atimed interruptions which will now be described.

Polar relay 913, upon'operating, closes ay circuit Yextending from ground at its lower armature and front contact, conductors 915 and 916 over two parallel paths, 1one extending through condenser 91"1-l and the upper winding of relay 918 and the.

other through'resistance A9i!! and'92ll and vthe `lower-winding of relayf918, resistance-921,con .Am other path alsov extends from a tap between resistances` 919 andf929 through resistance 922 to conductor NEG. `The current owing'through the lower winding of relay 918 tends to'operate the relay armature to its right-hand contact and that `flowing in theupper winding of the relay tends to hold the relay on the left-hand contact` as shown. -When the-charging currentyflowing through the upper windingof relay 918, decreases suiiiCien'tIy, thearmature ofthe relay moves'to 'itsright-hand contact -under'thecontrol of the current-owing inthe lower winding of the relay.

As soon'as theA armature ofrelay 918 closesto its right-hand contacts, the `current-in the lower winding is reversed, tending to drive the armature to its left-hand contact. The charge on condenser 911,V however, causes aY current flow L through the secondary winding of'relay' 918 in a direction tending to hold the armature oi relay 918 on its right-hand contacts. When the discharge current on 'condenser 911 is su'ciently, dissipated, the armature ofrelay'918 is driven to" its left-hand contact under thelinuence of the reversed current in the lower winding. When the right-hand contact. is opened, the reversed current in the lower windingof relay 918 ceases Y and the current through the Vupper winding and the operating current throught-,he lower winding again begins'to now causing` a repetition. of the completecycle. Relay ,918 therefore operates and releases at a rate of.,.about.nine.cycles,per

second.

'Relay vllll which. is normally held. infitsrighthand position `as shown under the influence .of the current nowng in its upper winding, receives av greatly increasedcurrent in the lower winding every time that theLleft-hand contacty orrelay` 918 is opened. The increasedurrentis aresult of the chargingo .condenser 91'1 .and is of sufficient value to .drive .thearmature -of relay 914 to its .left-hand contact. When this chargingY current has decreased -to a suicientlysmall value,.relay914.moves its .armature back to its right-hand contact. VvThe armatureof relay 914 remains .on` its left-hand .contact for approxi- .mately, .022 of a. second, thusasa result ofthe 1&1

action. of lrelays 91 Land 914;'.apulse' ofabout .022

lof a :second occurring nine times ,1 a -second is produced. ,Thissignal isz correctlyitimed topro-` :duce a seriesr of .Ksignals on the exchange office operatorsV teletypewriter.

All trunks 4busy In the even-of..all .trunks being busy when a subscriber served by the satelliteA attendant desires to originate a call, the satellite attendant,

will hold operatedthe key Aassociated with the calling'subscribers station, forrexample, either key 614 associated with station A .or key 81'1 associated withstation .B. VThe. key operated in this case transfersl the station line conductors to the afore-mentioned source of timedY interrupl tions .in a circuit traceable from motor generator set Plus, conductor. POS, battery tapresistance '923, through ,thewinding ofrelay 924, back contact-and upper.armature of relay 998, armature and right-hand contact of relay.914. shunted by upper back contacten. relay 913,. innerV lower armature and. back Contact of relay 908, conductor 924, .operated contact and right-hand spring memberof either oflkeys Y81'1 or'614 depending onthe subscribers station at which the call originated, .normally closed contacts and their respectively right-hand spring members of all the keys in series, over'the station line conductors, back throughtheinner left-hand spring member and normally closed contact of each of the' keys associated with .the .calling station, left-hand vspring memberand operated vcontact of either of. keys..81l.or Gill, conductors 848, and NEG to motor .generator.set.Minus. Relay 924 upon operating causesrelays 912.and 9131to .operatein turn. vRelay912,upon operating, also prevents from stopping the .motor generator. sets which were. started bythe operationof relay 1602 when the stationlloop wasfirst. closed. VRelay`912 is made- Vslow-to.release sothat.. it will remain operated i1.re1ay.v.921I follows the generation of the timed signals.

Remote control of the motor'jgeneator sets It was shown that conductor 1991 which is connected' to conductors 323, was `grounded in each trunk when .the operator 'atthe .exchange oce pluggedlin and rang and also when any station subscriber originated a call causing relay 1991 tooperate. Groundon conductor 1901 through the `winding of slow-to-release relay. i092 causes the relay tooperate andl thereby, in turn, operating relays 11394 and 1963. Relay 1903 upon operating connects the commercial source of electric power to motor generator sets Plus and Minus. These sets respectively provide a secondary ysource ofy positive `and negative telegraph voltage which is impressed `on-econductors POS '.andvNEG. .Relay 10M isla dash-.pot orV other Atype of-relay wl'iose 'operating time is .not less 4than the-timefor vthe -motor .generator sets to .reachlnormal speed. `i/xhenfrelay- 1G94 eventuale .'ly operates it'connects ground to .lead

1965. Whenthefdemand' forpowerceases ground is removed e from lconductor 1091 :thereby causing -relays' i992, 19133 `and |904 to'releasewhereby the motor generator sets-are stopped.

Remote control of the attendants teletypcwriter atthesatellite switching 'center v ItmvasshownY that conductor'SZll lwas 'grounded Ain .a vtruunk onan' ncomingtrunk call. This .ground causesY relayf9lll' to operate .and connects a cornmercialsource of power tothe. attendants 

